The present invention relates to a new and improved indicia disc and the manner in which it is made.
Indicia discs are commonly utilized in phototypesetting apparatus. Small discs are used in the form of unsupported photographic film. Commonly, a 7 mil polyethylene terephthalate disc is used as the film base, and an edge guide is used to stabilize the rotating disc. The indicia discs have previously been made by covering one side of a glass base member with a silver photo sensitive coating and forming transparent characters in the coating. Although the glass indicia discs have been satisfactory in operation, they are relatively fragile and expensive to replace if they become broken. Further, if the emulsion is scratched, the entire disc is destroyed.
The glass disc of the prior art practice is a carefully made glass plate, coated with emulsion, exposed and developed as a photographic negative, and then finished. The finishing steps include some sizing, drilling and polishing that are relatively high in damage risk.
Further, each font requires a separate disc.
To overcome the breakage problem, indicia discs have been made from relatively flexible sheets of plastic. Although the sheet plastic indicia discs are more durable than the glass indicia discs, the flexibility of the sheet plastic discs limits the distance at which fonts of characters can be disposed outwardly of the center portion of the discs. To overcome both the breakage problem inherent with the glass indicia discs and the flexibility problem of discs formed of sheets of plastic, a clamp arrangement has been utilized to hold a film disc in the manner disclosed in U.S. patent application Ser. No. 332,477, filed Feb. 14, 1973, by William Rosenstein and entitled Composite Photocomposing Font Disc, now U.S. Pat. No. 3,821,770. Also, guides have been employed to serve as stabilizers for film discs, but effective guides are expensive, and they must be cleaned of abraded disc bits.